Using Elephant Tusklessness as a Phenomenon to Engage Students About Evolution

When I first learned about the selection for tusklessness in African elephants, I immediately knew this was an engaging phenomenon for students. This compelling story of evolution address many misconceptions, including the idea that evolution is slow, requiring hundreds or thousands of generations. However, I wasn’t sure at first how to present the phenomenon. I was thrilled, therefore, when a few months later, BioInteractive released the video Selection for Tuskless Elephants. Ever since this video was released, it has been the center of student engagement for learning about evolution in my classroom.

I teach general biology, which is the first year of high school biology for my students. On the first day of our evolution unit, which occurs early in the year — long before we learn about genetics — we start with a discussion that probes for student understanding. Our conversation results in a working definition of evolution based on students’ prior knowledge. Generally, students suggest that evolution is something about change over generations in a population. Using this cursory definition as a launchpad for further learning, I ask them to imagine the animal a scientist is least likely to be able to observe evolving within the timeframe of the scientist’s research career. Sometimes it is necessary to remind the students to think about generation time — always, they come up with two ideas: whales and elephants.

Next, without introducing the concepts described in the video, I show the film Selection for Tuskless Elephants. Because we haven’t yet at this point discussed mechanisms that drive evolution, the scientific term “selection” means nothing to my students. They watch the film while responding to these simple prompts in their science notebooks.

• One thing I already knew was …
• One thing I was surprised by was …
• The most engaging part of this film was …
• One way this film changed my thinking is …
• One thing I wonder about is …

After the film is over and we have a brief discussion regarding their reflections, I pose the question “Is natural selection acting on the trait of tusklessness in elephants?” While student knowledge at this point is not deep enough to definitively answer this question, the question does raise a highly engaging idea. Elephant tusklessness and the effect of poaching generaties emotional responses for my students, as elephants are beloved creatures and the idea of humans killing them for their ivory is deeply upsetting.

This emotional investment in the question of elephant evolution drives student interest throughout the rest of the unit. We quickly move into studying one of the most important mechanisms driving evolution: natural selection. Using other BioInteractive resources, such as the Making of the Fittest films, students develop a deep, critical understanding of natural selection. For each example in the films, students learn to look for the following lines of evidence before concluding that natural selection is acting on a population.

• Is there evidence for variation in the trait of interest?
• Is there evidence that the trait is heritable?
• Is there evidence that there is differential fitness associated with the variants of that trait?
• Is there evidence of change over generations?

Next, we watch various Making of the Fittest films to challenge students to look for this evidence in different contexts. Natural Selection and Adaptation, which is about the evolution of the rock pocket mouse, is perhaps the most straightforward. Natural Selection in Humans and Got Lactase?, which are both about evolution in humans, add layers of complexity for the students as they look for evidence of natural selection. After each film, as well as other examples presented in class, students are asked to critically evaluate the evidence for natural selection and construct arguments supporting their claims.

When I am convinced that my students have achieved the ability to critically evaluate evidence for natural selection in a population, we return to the elephants. Students are asked to make a claim answering the question, “Is natural selection acting on the trait of tusklessness in elephants?” At this point, the students are often conflicted. They see that the hallmarks of natural selection are found in this example. However, they are often very uncomfortable applying the idea of “natural” to this example. The result is magic — vigorous debate charged with science knowledge and emotional investment.

This debate becomes the framework for my summative assessment for the unit, which follows the claim-evidence-reasoning (CER) structure. Students are invited to pick any example from class and write an essay in which they state a claim, present the evidence, and tie everything together in a way that demonstrates that they understand how natural selection works. While some students choose the rock pocket mouse, stickleback fish, or other animals from the Making of the Fittest films, most examples are focused on the elephants.

This assignment is time-intensive for both me and my students, but the results are worth the time and effort. The writing process generally takes four to five 40-minute class periods plus time outside of class for additional feedback and revisions. I scaffold the assignment for easy moments of review and feedback during the writing process. For instance, for the first due date, students need to provide a claim and the requisite evidence in bullet points. At this point, we usually do a gallery walk, so that all students have the benefit of seeing the work their peers have done as well as getting direct feedback. This also allows me to easily spot missing or misinterpreted evidence.

Next, students expand this information into a paragraph that we peer edit in class, which becomes the beginning of their essay. I have approached this differently, including gallery walks, sharing Google docs in class, and anonymous commenting on our class learning management pages. No matter what approach we take to peer editing, students are always required to make at least three comments: one thing they like; one thing they have a question or need clarification about; and one suggest they think the writer should consider adding or changing. After that, they write an additional paragraph for their essay that is the reasoning part of this assessment. This is the hardest part of the assignment for all students. Stating evidence while considering a checklist of necessary evidence for natural selection is relatively easy once the get the hang of it. Tying it all together to explain how natural selection works is much more difficult.

I read and comment on every aspect of the essay, and students rewrite it based on my feedback. Thus, I do not give the assignment a final grade until after the students have received direct feedback from me several times. I believe all of the commenting and revisions result in mastery for every student, whereas a graded test question just identifies who understands it and who does not … leaving the ones who did not with gaps in their knowledge.

I know now, more than ever before, that my students can do much more than just answer a few test questions well enough to demonstrate a cursory understanding. Instead, they can dive deeply into and really express their understanding of evolution by natural selection. This allows them to apply their understanding to new cases with confidence and success, as I require them to do on a formal summative assessments. As the year continues and we add new layers onto our understanding of evolution (such as genetics, sources of mutations, the science of heredity, and other ideas they are first introduced to while learning about evolution), it becomes clear that their learning is deep and lasting.

Students in my classroom have websites on which they publish their work for the world to read, and I would love to share a few excellent examples from this unit. You are welcome to visit their websites to see authentic work that resulted from their learning through the BioInteractive resources!

Rock Pocket Mouse: https://ikewalker.weebly.com/class-posts/natural-selection

Elephants: https://mcsegura.weebly.com/works/tuskless-elephants-natural-selection

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